It really depends on what juice you're vaping through it. Higher percentage VG juices and darker juices tend to gunk up the coils quicker. I use 70PG/30VG juices most of the time and I'll run anywhere from 5 to 8 mls of juice through them before I clean and dry burn. Basically I clean about once a day, I don't like the coil to get to dirty before I clean it.